The present invention is related to a method and a device for thermal spraying, especially of metals, for the coating of surfaces, wherein the material employed for coating is supplied in the form of a wire, molten and sprayed.
Devices of this kind are known in different designs. Thus, for example, manually operated spray guns are known in which two wires are mutually approached at an angle by feeding means in front of an atomizing gas nozzle, wherein an arc melting the wire material is produced between the wire ends.
It is also known to produce a melting flame within the spraying head by means of which the material to be sprayed is molten, wherein the molten particles are then transported by compressed air or the like onto the surface to be coated. Merely in an illustrative manner for arc technology, EP-0 239 585 B with further references may be mentioned.
The object of the invention has been to provide a method and a device for the spraying of metallic wire wherein at least one of the electrodes is not destroyed. A high efficiency, a low noise level and easy handling are to be ensured.
According to the invention, with the method and the device of the kind mentioned above, this object is achieved by producing the melting energy by a plasma arc, wherein the arc is formed between a non-melting stationary electrode and a melting electrode in the form of the wire, and the molten material is sprayed in the direction of wire feeding.
Torch heads with a plasma arc are as such known as cutting heads to be employed for the cutting of metal sheets and operated with compressed air. In this arc plasma cutting, the heat energy and the kinetic energy of an ionized gas column (plasma) are utilized to melt the metal and displace it from the cutting gap. This property is utilized by the invention in that the plasma arc is a compressed-air plasma arc, and a wire for atomizing is fed to such a plasma cutting head. Preferably, the arc is formed between a non-melting stationary electrode and a melting wire. The molten material is sprayed in the direction of wire feeding. The plasma arc is first ignited between the two electrodes. An electrically conductive wire takes the function of an electrode. After ignition, the wire, which is consuming away, is advanced accordingly.
Further embodiments of the invention can be seen from the dependent claims; in particular, as mentioned above, the torch head may be designed as a compressed-air plasma arc torch. Conveniently, the feeding nozzle for the wire with the atomizing gas is arranged at an angle with the center line of the plasma torch; for example, in a further embodiment, this angle between the wire feed and the plasma torch center line is about 75xc2x0.
Conveniently, the centric wire feed is surrounded by the atomizing gas nozzle in an annular arrangement.
It may be advantageous when an inert gas plasma torch is associated with the atomizing gas nozzle, and/or that a non-metallic wire can be associated with the atomizing gas nozzle for melting and spraying.
A particular advantage of the invention resides in the fact, inter alia, that a higher melting rate can be accomplished; the application efficiency can be increased by at least 10%, dust formation and evaporation of material being reduced.
In a further embodiment, depending on the application of the device according to the invention, at least two torch heads with associated wire feeding and atomizing gas nozzles may be provided. In this case, it is possible to supply different materials to the different torch heads and then to apply the mixture of materials to the surface to be coated.